This invention refers to a device for electrically connecting the electrical power source and heating conductors incorporated or imbedded in glass sheets, in particular rear window defrosters for automobiles.
It is known that glass sheets, in particular rear windows for automobiles, may be heated electrically in order to eliminate or avoid fogging, by means of resistances incorporated or embedded, for example by means of a serigraphic process, on the glass sheet itself.
The electric current is brought to the heating resistances by means of connection devices applied generally to a strip of conductive material placed on the glass, said connection device being provided with a terminal the transversal cross section of which is constant, for a fixed or movable connection with conducting leads connected to the power supply.
A device of said type is disclosed in U.S. Pat. No. 3,981,556.
It happens, however, that said connecting devices are frequently subject, during assembly operations, to forces applied to the free end, said forces being of variable directions and intensity, as a consequence of the assembly requirements and the experience of the operator.
The stresses generated by said forces, applied when the electrical terminals are connected to the power leads, discharge on the connection welding between the conductive strip and the metal terminals.
As the stresses involved are of extremely variable intensity in function of the assembly necessities, but also depend on the experience of the operator, it may happen at times that the metal plate becomes separated from the surface of the conductive strip to which it had been previously welded.
In particular, uncontrolled torque and tensile stresses applied to the terminal end may be responsible for said separation of the plate.
The tear of the weld damages the conductive strip appreciably, whereby one is forced to disassemble the rear window from the body of the car again.
In order to overcome this disadvantage, particular attention is placed during the operation of welding of the metal terminals to the conductive strip and particularly severe tests are established in order to guarantee the resistance of the weld itself to predetermined values of tension.
However it may happen that being the forces applied, as previously stated, of random varying direction and intensity, the stresses which act on the weld have different values and directions from those for which the resistance of the weld is guaranteed.
As a consequence in some cases, the terminal is torn off and the rear window defroster is damaged.